Transducer coils energizing scr gate circuit



Sept. 1, 1964 a. w. COPE 3,

TRANSDUCER CQILS ENERGIZING SCR GATE CIRCUIT Filed Nov. 2, 1961 P NIOWP N lzj lg '31 LOAD m :5

PULSE SOURCE INVENTOR. GEORGE W. COPE BY g 3) ATTYS,

i AGENT.

United States Patent the Navy Filed Nov. 2, 1961, Ser. No. 149,790 5 Claims. (Cl. 318-129) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a current pulse producing circuit, and more particularly to a circuit for providing high energy current pulses to the push-pull actuating (30118 of a transducer.

Transducers which convertelectrical energy into mechanical energy in the form of sound waves are presently employed in underwater target detecting and other systems, such as sonar. One of the well known transducers employs a mechanical sound producing element having a portion thereof constructed of a magnetic material, whereby this material is attracted by a magnetic field. A pair of coils, known as push-pull coils, are disposed on either side of the magnetic element so that, as current is passed through these coils, the mechanical element is pushed or pulled toward one of the two coils. When current pulses are provided alternatively to each of the two windings at a given frequency, the mechanical element is forced by the action of the coils to mechanically vibrate between the two at that frequency. The higher the energy of the sound. which is desired, the greater must be the amount of energy supplied to the coils.

In producing such high energy pulses of sound waves, certain difliculties have been encountered in constructing a suitable circuit to provide the high energy current pulses to the push-pull coils of the transducer. The use of the thyratron tube in furnishing high energy current pulses is well known in the art. However, the thyratron tube possessescertain inherent disadvantages, which limit its usefulness in the present application. The thyratron tube must be maintained in an upright position to effect proper operation thereof, which makes its use aboard ships somewhat questionable. Further, the thyratron does not exhibit the advantages of physical ruggedness or reliability and long operating life of solid state devices, which have become more important in military applications because of these advantages over vacuum tubes. Where high efiiciency is desirable in the operation of the current drive mechanism, the thyratron lacks such high efliciency due to the relatively large voltage drop across the tube and the further need of heating filaments within the tube, both of which dissipate considerable amounts of energy.

Transistor circuits may be employed to provide the necessary driving currents for the transducer. The transistors exhibit the necessary ruggedness and lack the requirement that they be placed in a particular position to insure their operation. Transistors, however, are limited in their ability to pass large currents therethrough especially at high frequencies due to the delay inherent in transistors'in switching from a non-conducing to a conducting state; this presents serious problems of energy dissipation within the transistor. In order to handle large current requirements by'transistors, it would be necessary to place a number of transistors in parallel, thus raising the cost of such a circuit accordingly.

An object of the present invention is to provide a current driving circuit capable of providing large amounts of current at selected frequencies to the push-pull driving coils of a transducer, such circuit being rugged and effi- 3,147,419 Patented Sept. 1, 1964 cient even at high frequencies and capable of use in a large variety of environments.

Various other objects and advantages may be apparent from the following description of one embodiment of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims. In the accompanying drawing:

FIG. 1 illustrates a silicon controlled rectifier as employed in the present invention; and

FIG. 2 is an illustration of a pulse driving circuit according to the invention.

In FIG. 1, a well known silicon controlled rectifier is shown connected in an operating circuit. The silicon controlled rectifier, as shown, consists of a PNPN silicon semi-conductor structure with two end terminals 11 and 12 and a gate terminal 13 thereon. A source of positive DC. current 14 is connected to the P region end terminal 11 and a load is attached to the other end terminal 12. Another source of DC. current 16, is connected through a switch 17 to provide a starting pulse to the gate terminal 13. The operation of the silicon controlled rectifier 10 is such that a non-conducting state is maintained until a starting pulse is received at the gate terminal 1.3. During this non-conducting condition, no current flows from the DC. current source 14 to the load 15. At such time that the switch 17 is closed momentarily to provide a starting current pulse from the source 16 to the gate terminal 13, the silicon controlled rectifier 10 is placed in a highly conductive state thereby passing current from the DC. source 14 to the load 15. When the silicon controlled rectifier is conducting, a very large amount of current is passed therethrough with minimum resistance, the voltage drop being in most cases no more than one volt. After the large current flow has been initiated by the starting pulse, the passage of current therethrough will continue as long as this current does not fall below a certain amount which is known as the holding current. Thus the current once started is self sustaining, very much in the manner of the current flow through a thyratron tube. If the impedance of the load 15 is not sufficient to lower the current flow below the level of the holding current value, it will become necessary to provide some means for so doing. An additional current source 18 is connected through switch 19 to the terminal 12 in a direction to provide a backward flow of current to prevent further conduction of the silicon controlled rectifier 10. At such time that the switch 19 is closed, the current flow through the silicon controlled rectifier 19 is reduced below the holding current value, at which time conduction ceases and the rectifier returns to its original non-conducting state until the receipt of another gate pulse at the gate terminal 13. It is not necessary here to discuss the theory of operation of the silicon controlled rectifier since such theory is now well known in the art.

In FIG. 2, a magnetic transducer element 21 is disposed between two actuating coils 22 and 23. The first actuating coil 22 is connected in a series circuit with a DC. source of current 24, a silicon controlled rectifier 25, and a storage capacitor 26. The storage capacitor 26 is connected in another series circuit, which is in parallel therewith, having the second actuating coil 23 and a second silicon controlled rectifier 27. A pulse source 28 has its two outputs connected to the gate terminals of the silicon controlled rectifiers 25 and 27; the pulse source 28 provides starting pulses in alternative fashion to first one silicon controlled rectifier and then the other at predetermined time intervals to drive the transducer element 21 at the desired frequency.

In operation, a first starting pulse is delivered from the pulse source 28 to the gating terminal of the first silicon controlled rectifier 25 to initiate conduction therein. The pulse from the source 28 need only be a very narrow pulse, such as is obtained from differentiating the leading edge of the pulses from a multivibrator circuit. The gating pulse initiates conduction in the silicon controlled rectifier 25 and the resistance thereof drops to a negligible value. The current provided by the source 24 passes through the silicon controlled rectifier 25, the first actuating coil 22, and thence to the storage capactior 26. The current through the actuating coil 22 continues to flow until such time as the capacitor has charged to its maximum value; due to the action of the series LC circuit of the actuating coil 22 and the capacitor 26, the voltage on the capacitor 26 will build up to a value substantially above the voltage of the source 24. As the capacitor 26 is charged to its maximum, the current in the series circuit will start to reverse direction. At such time, the current through the silicon controlled rectifier has dropped below the holding current value and the silicon controlled rectifier 25 is thus cut off. After the silicon controlled rectifier 25 has been cut off, a second pulse is delivered from the pulse source 28 to the gate terminal of the second silicon controlled rectifier 27 to initiate conduction therethrough. The positive charge which has been maintained on the capacitor 26 is now discharged through the second series circuit of the second actuating coil 23 and the silicon controlled rectifier 27. The current flow through the second actuating coil 23 continues until such time as the capacitor is fully charged in the opposite direction; the current through the silicon controlled rectifier 27 drops below the holding current value, thus turning off the silicon controlled rectifier and preventing a reverse current flow therethrough. When a second pulse is delivered to the first silicon controlled rectifier 25, conduction therethrough begins again thus initiating another cycle of operation. It is to be noted that on the second and subsequent cycles the storage capacitor 26 has a negative charge thereon at the beginning of the cycle; thus the total current flow through the first actuating coil 22 during the second and subsequent half cycles of operation will be greater than during the first cycle. As the current passes first through one actuating coil and then the other, the transducer magnetic element 21 is pulled first toward one and then toward the other of the coils in time with the pulses.

The pulse source 28 should deliver the initiating pulses to each of the silicon controlled rectifiers at just such time as would provide for maximum efliciency; this condition would closely correspond to the center position of the transducer element, as shown in FIG. 2. The length of these pulses is determined by the resonant frequency of the LC circuit composed of the storage capacitor 26 with each of the actuating coils 22 and 23. The LC time constant for both circuits should be made identical and should correspond to the desired pulse length which will give maximum efliciency as determined by the mechanical vibrating frequency of the transducer magnetic element 21. The movement of the transducer magnetic element 21 in relation to the coils effects a variable reluctance in the operation of the coils in the circuit. This factor must also be taken into account in designing the circuit for optimum operation, as will be evident to any person skilled in the art.

Thus it is seen that the circuit provides a low cost method of driving a variable reluctance transducer with high current values by using only a pair of silicon controlled rectifiers. The power loss in the circuit is also small due to the very low voltage drop across the silicon controlled rectifier in its conductive state. The fast switching time characteristics of the silicon controlled rectifier also make possible higher frequency operation of the variable reluctance transducer without the attendant power losses heretofore associated therewith.

It will be understood that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled i in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. A circuit for providing driving current to the actuating coils of a transducer comprising a first series circuit including a direct current power source, a first silicon controlled rectifier, a first current actuated element and storage capacitor means,

a second series circuit consisting of said storage capacitor means, a second current actuated element and a second silicon controlled rectifier,

and pulse means coupled to said first silicon controlled rectifier for initiating current flow in said first series circuit to charge said storage capacitor means in a first direction, said charge on said storage capacitor means in said first direction providing a reverse bias to said first silicon controlled rectifier to open said first series circuit including said direct current power supply and to forward bias said second silicon controlled rectifier,

said pulse means coupled to said second silicon controlled rectifier for initiating current fiow'in said second series circuit to charge said storage capacitor means in a direction opposite said first direction whereby driving current is supplied alternately to said first and second current actuated elements.

2. A circuit for providing driving current to the actuating coils of a transducer comprising a closed loop first series circuit including a direct current power supply, a first silicon controlled rectifier, a first actuating coil, and storage capacitor means,

a second series circuit connected across said storage capacitor means consisting of a second actuating coil and a second silicon controlled rectifier,

and pulse means for successively actuating said first and second silicon controlled rectifiers respectively, said pulse means coupled to said first silicon controlled rectifier for initiating current flow in said first series circuit to charge said storage capacitor means in a first direction, said first silicon controlled rectifier being reversed biased by said storage capacitor means being charged in said first direction to open said first closed loop series circuit thereby inactivating said direct current power supply,

said pulse means coupled to said second silicon controlled rectifier for closing said second series circuit for transmitting energy stored in said capacitor storage means and received from said direct current power supply during current flow in said first series circuit to said second actuating coil whereby said capacitor storage means is charged in a direction opposite to said first direction.

3. The combination in claim 2 wherein said capacitor storage means is a capacitor having first and second plates, said plates alternately receiving an opposite charge thereon uprlm alternate actuation of said first and second actuating 001 s.

4. A transducer driving circuit for providing driving current to the actuating coils of a transducer comprising a first series circuit including a first silicon controlled rectifier, a first current actuated element, and a capacitor storage means,

a second series circuit including said capacitor storage means, a second current actuated element and a second silicon controlled rectifier,

pulse means coupled to said first and second silicon controlled rectifiers for alternately initiating conduction in said first and second series circuits to alternately provide a driving current to said first and sec ond current actuated elements, said capacitor storage means being charged in opposite directions upon separate actuation of each of said first and second current actuated elements, and a single power source, said power source connected in said first series circuit for supplying driving power to said first and second series circuits during alternate current conduction in each of said first and second series circuits.

5 A circuit for providing driving current to the actuating coils of a transducer comprising a first series circuit including a direct current power source, a first silicon controlled rectifier, a first actuating coil and storage capacitor means,

said storage capacitor means directly interconnecting one terminal of said direct current power source and one terminal of said first actuating coil,

a second series circuit including said storage capacitor means, a second actuating coil and a second silicon controlled rectifier,

and pulse means coupled to said first silicon controlled rectifier for initiating current flow in said first series circuit to charge said capacitor means in a first direction, said first direction of charge on said storage capacitor means providing a reverse bias to said first silicon controlled rectifier to open said first series circuit including said direct current power source and to forward bias said second silicon controlled rectifier,

said pulse means coupled to said second silicon controlled rectifier for initiating current flow in said second series circuit to charge said storage capacitor means in a direction opposite to said first direction whereby driving current is supplied alternately to said first and second actuating coils.

edition, copyright 1960 by the GE. Co., FIG. 8.47, page 143. 

1. A CIRCUIT FOR PROVIDING DRIVING CURRENT TO THE ACTUATING COILS OF A TRANSDUCER COMPRISING A FIRST SERIES CIRCUIT INCLUDING A DIRECT CURRENT POWER SOURCE, A FIRST SILICON CONTROLLED RECTIFIER, A FIRST CURRENT ACTUATED ELEMENT AND STORAGE CAPACITOR MEANS, A SECOND SERIES CIRCUIT CONSISTING OF SAID STORAGE CAPACITOR MEANS, A SECOND CURRENT ACTUATED ELEMENT AND A SECOND SILICON CONTROLLED RECTIFIER, AND PULSE MEANS COUPLED TO SAID FIRST SILICON CONTROLLED RECTIFIER FOR INITIATING CURRENT FLOW IN SAID FIRST SERIES CIRCUIT TO CHARGE SAID STORAGE CAPACITOR MEANS IN A FIRST DIRECTION, SAID CHARGE ON SAID STORAGE CAPACITOR MEANS IN SAID FIRST DIRECTION PROVIDING A REVERSE BIAS TO SAID FIRST SILICON CONTROLLED RECTIFIER TO OPEN SAID FIRST SERIES CIRCUIT INCLUDING SAID DIRECT CURRENT POWER SUPPLY AND TO FORWARD BIAS SAID SECOND SILICON CONTROLLED RECTIFIER, SAID PULSE MEANS COUPLED TO SAID SECOND SILICON CONTROLLED RECTIFIER FOR INITIATING CURRENT FLOW IN SAID SECOND SERIES CIRCUIT TO CHARGE SAID STORAGE CAPACITOR MEANS IN A DIRECTION OPPOSITE SAID FIRST DIRECTION WHEREBY DRIVING CURRENT IS SUPPLIED ALTERNATELY TO SAID FIRST AND SECOND CURRENT ACTUATED ELEMENTS. 